The following invention relates to a labyrinth seal for use in electronic spindle motors having ball bearing rings.
As shown in FIG. 1, electric spindle motors of the type used in disk drives conventionally use ball bearing rings 18 to facilitate movement between a rotary member and a stationary member. Ball bearing rings 18 generally include metallic or ceramic ball bearings 20 which are positioned between an inner bearing ring 22 and an outer bearing ring 24. Bearing rings 18 may be either inner or outer rotators depending on whether the hub 26 or shaft 28 rotates. Inner rotators have an inner bearing ring 22 which rotates, and outer rotators have an outer bearing ring 24 which rotates. The ball bearings 20 are preferably evenly spaced within the inner and outer bearing rings 22 and 24. The ball bearings 20 are generally held in this evenly spaced position by teeth of a ball bearing cage (not shown).
Bearing lubricant fluid is used in bearing rings 18 to encourage free movement of the ball bearings 20, inner bearing ring 22, and outer bearing ring 24. Conventionally, the lubricant is initially deposited on the teeth of the bearing cage. During use, however, the lubricant tends to migrate and eventually escapes the bearing ring 18. The lubricant that migrates and escapes the bearing ring 18 often enters the interior of the motor or exits the motor completely.
One cause of lubricant migration is the rotation of the bearing ring 18 and gravitational pull that causes the lubricant to be thrown from the bearing ring 18. Although lubricant generally is not thrown from a bearing ring 18 at lower rotation speeds, higher rotation speeds tend to disperse or "sling out" lubricant. At particularly high speeds the lubrication is atomized.
Another cause of lubricant migration is airflow through the motor and bearing rings 18 which tends to push lubricant, particularly atomized lubricant, out of the bearing ring 18. Airflow also tends to carry particles and contaminants. The use of bearing shields 30 reduces the flow of air and contaminants through the bearing ring 18 and thereby partially inhibits the loss of lubricant from the bearing ring 18.
Once the lubricant escapes the bearing ring 18 it enters the horizontal gap 32 between the top surface of the ball bearing ring 18 and the bottom surface of the washer 34 (or other enclosing apparatus). The lubricant then travels from the gap 32 up through the vertical air gap 36 between the inner surface 38 of the washer 34 and the smooth outer surface 39 of the shaft 28. The lubricant then can escape the motor.
Using fluid labyrinths to prevent lubrication fluid from escaping a fluid bearing spindle motor is shown in U.S. Pat. No. 5,536,088 which is assigned to the same assignee as the present application, the disclosure of which is hereby incorporated by reference. Fluid labyrinths found in such fluid bearing spindle motors are generally the winding path in which the lubrication fluid resides, at least part of which forms the fluid bearings.
Fluid labyrinths are not used with ball bearing spindle motors because the lubrication fluid is not intended as a bearing but instead is used to facilitate rotation between the ball bearings 20 and the inner and outer bearing rings 20, 24. Accordingly, the lubrication fluid is not intended to enter the air gaps 32 and 36.